Abstract. Studies of distant galaxies have shown that ellipticals and large spirals (Schade et al. 1999, ApJ, 525, 31; Lilly et al. 1998, ApJ, 500, 75) were already in place 8 Gyr ago, leading to a very modest recent star formation (Brinchmann & Ellis 2000, ApJ, 536, L77) in intermediate mass galaxies (3−30 × 10 10 M ). This is challenged by a recent analysis (Heavens et al. 2004, Nature, 428, 625) of the fossil record of the stellar populations of ∼10 5 nearby galaxies, which shows that intermediate mass galaxies formed or assembled the bulk of their stars 4 to 8 Gyr ago. Here we present direct observational evidence supporting this findings from a long term, multi-wavelength study of 195 z > 0.4 intermediate mass galaxies, mostly selected from the Canada France Redshift Survey (CFRS). We show that recent and efficient star formation is revealed at IR wavelengths since ∼15% of intermediate mass galaxies at z > 0.4 are indeed luminous IR galaxies (LIRGs), a phenomenon far more common than in the local Universe. The star formation in LIRGs is sufficient in itself to produce 38% of the total stellar mass of intermediate mass galaxies and then to account for most of the reported stellar mass formation since z = 1. Observations of distant galaxies have also the potential to resolve their star formation and mass assembly histories. The high occurrence of LIRGs is easily understood only if they correspond to episodic peaks of star formation, during which galaxies are reddened through short IREs (infrared episodes). We estimate that each galaxy should experience 4 to 5 × (τ IRE /0.1 Gyr) −1IREs from z = 1 to z = 0.4, τ IRE being the characteristic timescale. An efficient and episodic star formation is further supported by the luminosity-metallicity relation of z ∼ 0.7 emission line galaxies, which we find to be on average metal deficient by a factor of ∼2 when compared to those of local spirals. We then examine how galaxy IREs can be related to the emergence at high redshift of the abundant population of galaxies with small size (but not with small mass), blue core and many irregularities. We show that recent merging and gas infall naturally explain both morphological changes and episodic star formation history in a hierarchical galaxy formation frame. We propose a simple scenario in which 75 ± 25% of intermediate mass spirals have recently experienced their last major merger event, leading to a drastic reshaping of their bulges and disks during the last 8 Gyr. It links in a simple manner distant and local galaxies, and gives account of the simultaneous decreases during that period, of the cosmic star formation density, of the merger rate, and of the number densities of LIRGs, compact and irregular galaxies, while the densities of ellipticals and large spirals are essentially unaffected. It predicts that 42, 22 and 36% of the IR (episodic) star formation density is related to major mergers, minor mergers and gas infall, respectively.

Using the multi-integral field spectrograph GIRAFFE at VLT, we have derived the K-band Tully-Fisher relation (TFR) at z ∼ 0.6 for a representative sample of 65 galaxies with emission lines (W 0 (OII) ≥ 15 Å). We confirm that the scatter in the z ∼ 0.6 TFR is caused by galaxies with anomalous kinematics, and find a positive and strong correlation between the complexity of the kinematics and the scatter that they contribute to the TFR. Considering only relaxed-rotating disks, the scatter, and possibly also the slope, of the TFR, do not appear to evolve with redshift. We detect an evolution of the K-band TFR zero point between z ∼ 0.6 and z = 0, which, if interpreted as an evolution of the K-band luminosity of rotating disks, would imply that a brightening of 0.66 ± 0.14 mag occurs between z ∼ 0.6 and z = 0. Any disagreement with the results of Flores et al. (2006, A&A, 455, 107) are attributed to both an improvement of the local TFR and the more detailed accurate measurement of the rotation velocities in the distant sample. Most of the uncertainty can be explained by the relatively coarse spatial-resolution of the kinematical data. Because most rotating disks at z ∼ 0.6 are unlikely to experience further merging events, one may assume that their rotational velocity, which is taken as a proxy of the total mass, does not evolve dramatically. If true, our result implies that rotating disks observed at z ∼ 0.6 are rapidly transforming their gas into stars, to be able to double their stellar masses and be observed on the TFR at z = 0. The rotating disks observed are indeed emission-line galaxies that are either starbursts or LIRGs, which implies that they are forming stars at a high rate. Thus, a significant fraction of the rotating disks are forming the bulk of their stars within 6 to 8 Gyr, in good agreement with former studies of the evolution of the mass-metallicity relationship.

Abstract.To determine the population membership of nearby stars we explore abundance results obtained for the light neutronrich elements 23 Na and 27 Al in a small sample of moderately metal-poor stars. Spectroscopic observations are limited to the solar neighbourhood so that gravities can be determined from H parallaxes, and the results are confronted with those for a separate sample of more metal-poor typical halo stars. Following earlier investigations, the abundances of Na, Mg and Al have been derived from NLTE statistical equilibrium calculations used as input to line profile synthesis. We do not confirm the age gap between thin and thick disk found by Fuhrmann. Instead we find an age boundary between halo and thick disk stars, however, with an absolute value of 14 Gyr that must be considered as preliminary. While the stellar sample is by no means complete, the resulting abundances indicate the necessity to revise current models of chemical evolution and/or stellar nucleosynthesis to allow for an adequate production of neutron-rich species in early stellar generations.

A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to-noise ratios (SNR) on the measurement of the stellar atmospheric parameters (effective temperature T eff , surface gravity log g, and metallicity [Fe/H]). We show that ULySS is reliable to determine these parameters with medium-resolution spectra (R∼2000). Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope (GSJT). The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline (SSPP), and we derived precisions of 167 K, 0.34 dex, and 0.16 dex for T eff , log g and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectra template library (Version 1.0) of GSJT, and will be deployed as basic ingredients for the GSJT automated parametrization pipeline.

Nearly half the stellar mass of present-day spiral galaxies has formed since z = 1, and galaxy kinematics is an ideal tool to identify the underlying mechanisms responsible for the galaxy mass assembly since that epoch. Here, we present the first results of the ESO large program, "IMAGES", which aims at obtaining robust measurements of the kinematics of distant galaxies using the multi-IFU mode of GIRAFFE on the VLT. 3D spectroscopy is essential to robustly measure the often distorted kinematics of distant galaxies (e.g., Flores et al. 2006, A&A, 455, 107). We derive the velocity fields and σ-maps of 36 galaxies at 0.4 < z < 0. 10 M emission line galaxies in this redshift range, and are largely unaffected by cosmic variance. Taking into account all galaxies -with or without emission lines -in that redshift range, we find that at least 41 ± 7% of them have anomalous kinematics, i.e., they are not dynamically relaxed. This includes 26 ± 7% of distant galaxies with complex kinematics, i.e., they are not simply pressure or rotationally supported. Our result implies that galaxy kinematics are among the most rapidly evolving properties, because locally, only a few percent of the galaxies in this mass range have complex kinematics. It is well-established that galaxies undergoing a merger have complex large-scale motions and thus are likely responsible for the strong evolution of the galaxy kinematics that we observe.

Aims. Our aims are to estimate the validity of empirical methods, such as R 23 , R 23 − P, log([N ii]/Hα) (N2), log[([O iii]/Hβ)/ ([N ii]/Hα)] (O3N2), and log([S ii]/Hα) (S2), and to re-derive (or add) the calibrations of R 23 , N2, O3N2, and S2 indices for oxygen abundances on the basis of a large sample of galaxies with T e -based abundances.Methods. We determined the gas-phase oxygen abundance for a sample of 695 galaxies and H ii regions with reliable detections of [O iii]4363, using the reliable and direct temperature-sensitive (T e ) method of measuring metallicity. We selected 531 star-forming galaxies from the SDSS-DR4 database with strong emission lines, including [O iii]4363 detected at a signal-to-noise ratio higher than 5σ, as well as 164 galaxies and H ii regions from the literature with T e measurements. The O/H abundances were derived from a two-zone model for the temperature structure, assuming a relationship between high ionization and low ionization species. Results. We compare our (O/H) Te measurements of the SDSS sample with the abundances obtained by the MPA/JHU group who used multiple strong emission lines and Bayesian techniques (Tremonti et al. 2004). For roughly half of the sample the Bayesian abundances are overestimated ∼0.34 dex, possibly due to the treatment of nitrogen enrichment in the models they used. The R 23 and R 23 − P methods systematically overestimate the O/H abundance by a factor of ∼0.20 dex and ∼0.06 dex, respectively. The N2 index, rather than the O3N2 index, provides more consistent O/H abundances with the T e -method, but with some scatter. The relations of N2, O3N2, and S2 with log(O/H) are consistent with the photoionization model calculations of Kewley & Doptita (2002), but R 23 does not match well. We derive analytical calibrations for O/H from R 23 , N2, O3N2, and S2 indices on the basis of this large sample, including the excitation parameter P as an additional parameter in the N2 calibration. These empirical calibrations are free of the systematic problems inherent in abundance calibrations based on photoionization models. Conclusions. We conclude that the N2, O3N2, and S2 indices are useful indicators for calibrating metallicities of galaxies with 12 + log(O/H) < 8.5 and that the R 23 index works well for the metal-poor galaxies with 12+log(O/H) < 7.9. For the intermediate metallicity range (7.9 < 12 + log(O/H) < 8.4), the R 23 and R 23 − P methods are unreliable for characterizing the O/H abundances,

Abstract. One hundred and five 15 µm-selected objects in three ISO (Infrared Space Observatory) deep survey fields (CFRS 3 h , UDSR and UDSF) are studied on the basis of their high-quality optical spectra with resolution R > 1000 from VLT/FORS2. ∼92 objects (88%) have secure redshifts, ranging from 0 to 1.16 with a median value of z med = 0.587. Considerable care is taken in estimating the extinction properties of individual galaxy, which can seriously affect diagnostic diagrams and estimates of star formation rates (SFRs) and of metal abundances. Two independent estimates of the extinction have been made, e.g. Balmer line ratio and energy balance between infrared (IR) and Hβ luminosities. For most of the sources, we find a good agreement between the two extinction coefficients (within ±0.64 rms in A V , the extinction in V band), with median values of A V (IR) = 2.36 and A V (Balmer) = 1.82 for z > 0.4 luminous IR galaxies (LIRGs). At z > 0.4, our sample show many properties (IR luminosity, continuum color, ionization and extinction) strikingly in common with those of local (IRAS) LIRGs studied by Veilleux et al. (1995). Thus, our sample can provide a good representation of LIRGs in the distant Universe. We confirm that most (>77%) ISO 15 µm-selected galaxies are dominated by star formation. Oxygen abundances in interstellar medium in the galaxies are estimated from the extinction-corrected "strong" emission line ratios (e.g. . Their properties can be reproduced with infall models although one has to limit the infall time to avoid overproduction of metals at late times. The models predict that total masses (gas + stars) of the distant LIRGs are from 10 11 M to ≤10 12 M . A significant fraction of distant large disks are indeed LIRGs. Such massive disks could have formed ∼50% of their metals and stellar masses since z ∼ 1.

Context. This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to a redshift of one. Intermediate mass galaxies (M J ≤ −20.3) are selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts. Aims. Our primary aim in this study is therefore to obtain a sample of intermediate-mass galaxies with known spectroscopic redshift to be used for further analysis of their 3D-kinematics. We also intend to test whether this important cosmological field may be significantly affected by cosmic variance. Methods. The spectroscopic observations were carried out using VIMOS on the ESO VLT. The data reduction was done using a set of semi-automatic IRAF procedures developed by our team. Results. We have spectroscopically identified 691 objects including 580 galaxies, 7 QSOs, and 104 stars. The overall completeness achieved is about 76% for objects with I AB ≤ 23.5 in the CDFS after excluding instrumental failures. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large-scale structures in the CDFS, which are found to be more prominent than in other redshift surveys. To test the impact of these structures in the GOODS-South field, we constructed a representative redshift catalog of 640 galaxies with I AB ≤ 23.5 and z ≤ 1. We then compared the evolution of rest-frame U, B, V, and K galaxy luminosity densities to the one derived from the Canada France Redshift Survey (CFRS). The GOODS South field shows a significant excess of luminosity densities in the z = 0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 µm. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large-scale structures at z = 0.668 and at z = 0.735, which contain a significant excess of evolved, massive galaxies when compared to other fields. Conclusions. This leads to a clear warning about the results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities that are apparently less affected by cosmic variance (0.25 dex at 2.1 µm), however, at the cost of any ease in disentangling the evolutionary and cosmic variance effects.